A heterogeneous body structure is a body structure that includes a plurality of different parts or different types of parts, wherein properties within one part of the body structure are different from properties of other parts of the body structure. Further, heterogeneous body structures exhibit spatial variation in the aforementioned properties. In other words, a heterogeneous body structure is in particular anisotropic.
Biological tissues such as, for example, the brain or liver, are generally heterogeneous body structures that exhibit varying properties. In heterogenous body structures, an injected substance does not spread isotropically around the injection location. The target region at which the medical drug acts can therefore differ significantly from the injection point at which the medical drug is injected. This effect is caused by the heterogeneity and the different physical and physiological properties of the body structures in question. These differences can be present in a healthy body structure (e.g., anatomical, biological and/or physiological properties of the body structures) or can be generated or compounded by illnesses (e.g., from a tumor or bleeding). The vascularity of a tumor, for example, is very complex. The cells and vessels newly formed by the tumor can differ significantly in their properties from the cells and vessels of the healthy tissue. Blood vessels in a brain tumor for example, in particular in glial blastomata, do not have a functionally effective blood-brain barrier. For instance, the number of endothelial vesicles may be significantly increased in glial blastomata, and gaps may be found in the endothelial layer. In general, a significant change in the extra-cellular matrix of pathological vessels is seen in glial blastomata (the healthy brain includes cavities and folds which influence the distribution of fluid).
In the past, the aforementioned peculiarities of heterogeneous body structures have led to failures in the targeted local chemotherapy of glial blastomata in the brain. While laboratory experiments were significantly successful, this could not be repeated in humans. This was substantially due to the fact that the medical drug (in particular a chemotherapeutic agent in the case of glial blastomata) did not spread or did not sufficiently spread in the desired target region due to the heterogeneity of the brain, but was rather misdirected by the heterogeneity of the tissue. This can lead to problems in so-called CED pressure-driven drug dispensing (convection-enhanced delivery) for treating brain tumors.